1. Field of the Invention
The present invention relates to an alignment mark and an alignment mark design method by which wafers are aligned to correspond with masks in an exposure aligning system.
2. Description of the Related Art
Generally, semiconductor devices are fabricated by performing repeated and selective processes such as patterning, etching, diffusing, metal-deposition, etc., to form one or more circuit patterning layers on a wafer. The deposition of circuit patterning layers requires that previously formed circuit patterning layers be aligned accurately.
In the alignment relationship of wafers, the alignment marks formed on exposure field regions EFn or scribe lines SCL of a wafer are illuminated by a light source and reflect diffracted light rays. The diffracted light rays from the alignment marks are detected to generate a photoelectric signal which is used to detect the position of the wafer. The position state of the wafers is checked and the wafers are aligned by an alignment means to meet predetermined reference positions to complete the alignment of the wafers.
In such a conventional technique, the alignment marks shown in FIGS. 1A to 2B are used in a through the lens (TTL) type of field image alignment system in which a red color laser beam (633 nm) is used, and are generally formed of patterns in which a plurality of unit marks are aligned at both sides of the reference position thereof.
The unit mark of the alignment marks shown in FIG. 1 has a width of about 6 to 8.5 and length (l) of about 30 to 40 in a rectangular form. The gap Q between the unit marks is in the range of about 6 to 8.5 to which the width (t) of the unit mark is similar in the aligning direction of the plurality of unit marks. The pitch (P) is in the range of about 12xcx9c17.
If these alignment marks are changed in form in the course of performing various process steps, or covered with process layers including metal layers, there is a problem that both sides of the unit mark are not in a symmetrical form (asymmetry), as shown in FIG. 3. Such an asymmetrical form in the unit mark causes a range of error (d) in the position detection as shown in FIG. 4, which shows a graph illustrating the relationship of detected positions to a signal waveform (contrast).
In addition, the aforementioned unit mark has therein a dishing phenomenon by which its center position gets depressed compared with both end sides of the unit mark during a chemical mechanical polishing CMP process, as shown in FIG. 5 or 6. This phenomenon also causes the range of error (dxe2x80x2) in the position detection of the alignment mark, as shown in FIG. 7, which shows a graph illustrating the relationship of the position detection by contrast.
In an attempt to solve such problems, Korea Patent Application No. 10-2000-47405 discloses changing a conventional rectangular type of unit mark alignment pattern to a matrix type in the alignment marks. However, such a technique cannot be performed on a conventional alignment system. In addition, there is a problem that accuracy in measurement of alignment position is low, and reliability in the position detection is also reduced because the position of the alignment marks is measured by using a predetermined single wavelength of light that does not affect the sensitivity to light of photoresist.
In order to solve the aforementioned problems, an object of the present invention is to provide an alignment mark and an aligning method using the same, which can be implemented in a conventional alignment system. Each of the unit marks forming the alignment marks is further formed of a mesa or trench pattern therein so as to have detection signals of high order diffraction beams using different type wavelength beams, thereby resulting in more accurate alignment marks.
In addition, another object of the present invention is to provide an alignment mark and an aligning method using the same by which a dishing phenomenon and the resultant alignment error, occurring as a result of a chemical mechanical polishing process, can be prevented.
In accordance with the invention, the alignment mark of the invention includes a plurality of mesa or trench type unit marks aligned in line and spaced apart from one another with a predetermined gap therebetween formed in an underling layer to which a chemical mechanical polishing process is applied. Alignment signals are formed during an alignment process. The unit mark is made by aligning at least one or more mesa or trench patterns in order to prevent a dishing phenomenon during a chemical mechanical polishing process.
The mesa patterns can be formed with a predetermined pitch within the trench type of unit mark, and the trench patterns can be formed with a predetermined pitch within the mesa type of unit mark. Alignment signals from each of the unit marks are formed by at least three or more diffraction beam orders.
The mesa patterns or trench patterns can be parallel to the lengthwise direction of the unit mark and aligned in a width direction of the unit mark, relative to the rectangular form of unit mark having a predetermined length and width.
The pattern of pitch Pxe2x80x2 of the mesa or trench pattern is determined by the formula,
Pxe2x80x2=P/(2nxe2x80x2+1)xc2x10.05 xcexcm (nxe2x80x2: natural number), 
wherein P sin xcex8=nxcex, P: pitch between unit marks, xcex: wave length of laser beam, xcex8: diffraction angle, nxe2x80x2: the number of mesa or trench patterns, n: diffraction order of unit mark, xcexxe2x80x2: wave length of different laser beam for illuminating the mesa or trench patterns, 2nxe2x80x2+1: diffraction order by the wave length xcexxe2x80x2 of different lasers.
In addition, in one embodiment, when the pitch P between the unit marks is in the range of 7.9 to 8.2 xcexcm, the pattern width txe2x80x2 and pattern pitch Pxe2x80x2 of the mesa or trench patterns are formed in the range of 2.65-2.67 xcexcm and in the range of 5-5.4 xcexcm, respectively, when the diffraction order 2nxe2x80x2+1 is 3. The pattern width txe2x80x2 and the pattern pitch Pxe2x80x2 of the mesa or trench patterns can be formed in the range of 1.59-1.61 xcexcm and in the range of 3.1-3.3 xcexcm, respectively, when the diffraction order 2nxe2x80x2+1 is 5. The pattern width txe2x80x2 and pattern pitch Pxe2x80x2 of the mesa or trench patterns are formed in the range of 1.13-1.15 xcexcm and in the range of 2.27-2.29 xcexcm, respectively, when the diffraction order 2nxe2x80x2+1 is 7.
In accordance with the alignment method according to the present invention, mesa or trench patterns are aligned for forming a reverse image on each of mesa or trench type of unit marks. A first probing beam generating means and a second probing generating means are provided for illuminating the unit marks. Each of the unit marks aligned with the first probing beam is illuminated to confirm contrast between each of the unit marks and non-marked portions. Each of the unit marks is illuminated with the second probing beam to thereby confirm contrast between portions formed and portions not formed with the mesa or trench patterns. A mark center is determined by each of contrast values measured through the first and second probing beams.
In one embodiment, the first probing beam is a red color laser beam having an approximate 633 nm-wavelength band by which photoresist coating a wafer cannot be sensitized, and the second probing beam is a green color laser beam having a 532 nm-wavelength band by which photoresist coating a wafer cannot be sensitized.
The mark center position can be determined based on a maximum contrast value among the contrast values measured by illuminating the unit marks with the first probing beam and by illuminating the mesa or trench pattern with the second probing beam. Alternatively, the mark center position can be determined based on an average contrast value measured by illuminating the unit marks with the first probing beam and by illuminating the mesa or trench pattern with the second probing beam. In another alternative embodiment, the mark center position can be determined based on only the maximum contrast value measured by illuminating the mesa or trench pattern with the second probing beam, or determined based on only the average contrast value measured by illuminating the mesa or trench pattern with the second probing beam.